[OpenMap Users] Google Maps Projection

From: Christopher Mueller <cmueller_at_asascience.com>
Date: Mon, 8 Mar 2010 11:06:37 -0500

All,

I have successfully implemented a WMS provider that utilizes openmap to render the images from various datasets. However, I am running into a problem projecting the image into the "Google Projection" (EPSG:900913). I have tried using the built in "CoordinateReferenceSystem.getCode("EPSG:900913")" to generate the needed GeoProj object, but it appears to be exactly the same as the "normal" Mercator projection. The images produced when using the two projections are identical.

After some digging, I found the following resources, all of which allude to the "trick" being "nulling the nadgrid" - which essentially means NOT applying the WGS84 shift after translating from Meters.

http://docs.codehaus.org/display/GEOTDOC/Google+Maps+Projection
http://crschmidt.net/blog/archives/238/understanding-googles-projection-slightly-anyway/
http://www.sharpgis.net/post/2008/05/SphericalWeb-Mercator-EPSG-code-3785.aspx

The last link also indicates that the EPSG governing body has officially added the "Spherical Mercator / Web Mercator" projection to it's database - EPSG: 3785.

So there seems to be enough information to replicate the projection properly - the issue is, I can't seem to find the right hook to get the projection correct in openmap.

Has anyone out there successfully made the "Google Projection" work in openmap??

Thanks in advance for any help,

Best,

Chris


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Received on Mon Mar 08 2010 - 11:14:40 EST

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